Vertically aligned ZnO nanorod core-polypyrrole conducting polymer sheath and nanotube arrays for electrochemical supercapacitor energy storage

Nanoscale Research Letters, Sep 2014

Nanocomposite electrodes having three-dimensional (3-D) nanoscale architecture comprising of vertically aligned ZnO nanorod array core-polypyrrole (PPy) conducting polymer sheath and the vertical PPy nanotube arrays have been investigated for supercapacitor energy storage. The electrodes in the ZnO nanorod core-PPy sheath structure are formed by preferential nucleation and deposition of PPy layer over hydrothermally synthesized vertical ZnO nanorod array by controlled pulsed current electropolymerization of pyrrole monomer under surfactant action. The vertical PPy nanotube arrays of different tube diameter are created by selective etching of the ZnO nanorod core in ammonia solution for different periods. Cyclic voltammetry studies show high areal-specific capacitance approximately 240 mF.cm-2 for open pore and approximately 180 mF.cm-2 for narrow 30-to-36-nm diameter PPy nanotube arrays attributed to intensive faradic processes arising from enhanced access of electrolyte ions through nanotube interior and exterior. Impedance spectroscopy studies show that capacitive response extends over larger frequency domain in electrodes with PPy nanotube structure. Simulation of Nyquist plots by electrical equivalent circuit modeling establishes that 3-D nanostructure is better represented by constant phase element which accounts for the inhomogeneous electrochemical redox processes. Charge-discharge studies at different current densities establish that kinetics of the redox process in PPy nanotube electrode is due to the limitation on electron transport rather than the diffusive process of electrolyte ions. The PPy nanotube electrodes show deep discharge capability with high coulomb efficiency and long-term charge-discharge cyclic studies show nondegrading performance of the specific areal capacitance tested for 5,000 cycles.

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Vertically aligned ZnO nanorod core-polypyrrole conducting polymer sheath and nanotube arrays for electrochemical supercapacitor energy storage

Nanoscale Research Letters Vertically aligned ZnO nanorod core-polypyrrole conducting polymer sheath and nanotube arrays for electrochemical supercapacitor energy storage Navjot Kaur Sidhu 0 1 2 Alok C Rastogi 0 1 2 0 Electrical and Computer Engineering Department and Center for Autonomous Solar Power (CASP), Binghamton University, State University of New York , New York 13902 , USA 1 Open PPy nanotube (4-h etch) 2 Authors' information NKS is presently a PhD student at the Electrical and Computer Engineering Department at the State University of New York, Binghamton. ACR is Associate Professor at the Electrical and Computer Engineering Department and Associate Director of the Center for Autonomous Solar Power (CASP) at the State University of New York , Binghamton Nanocomposite electrodes having three-dimensional (3-D) nanoscale architecture comprising of vertically aligned ZnO nanorod array core-polypyrrole (PPy) conducting polymer sheath and the vertical PPy nanotube arrays have been investigated for supercapacitor energy storage. The electrodes in the ZnO nanorod core-PPy sheath structure are formed by preferential nucleation and deposition of PPy layer over hydrothermally synthesized vertical ZnO nanorod array by controlled pulsed current electropolymerization of pyrrole monomer under surfactant action. The vertical PPy nanotube arrays of different tube diameter are created by selective etching of the ZnO nanorod core in ammonia solution for different periods. Cyclic voltammetry studies show high areal-specific capacitance approximately 240 mF.cm−2 for open pore and approximately 180 mF.cm−2 for narrow 30-to-36-nm diameter PPy nanotube arrays attributed to intensive faradic processes arising from enhanced access of electrolyte ions through nanotube interior and exterior. Impedance spectroscopy studies show that capacitive response extends over larger frequency domain in electrodes with PPy nanotube structure. Simulation of Nyquist plots by electrical equivalent circuit modeling establishes that 3-D nanostructure is better represented by constant phase element which accounts for the inhomogeneous electrochemical redox processes. Charge-discharge studies at different current densities establish that kinetics of the redox process in PPy nanotube electrode is due to the limitation on electron transport rather than the diffusive process of electrolyte ions. The PPy nanotube electrodes show deep discharge capability with high coulomb efficiency and long-term charge-discharge cyclic studies show nondegrading performance of the specific areal capacitance tested for 5,000 cycles. Zinc oxide nanorods; Polypyrrole nanotubes; 3-D nanostructures; Supercapacitor; Pulsed electrochemical polymerization; Electrochemical energy storage; Redox capacitance - Background Electrochemical energy storage in the ultracapacitor devices is emerging as a frontline technology for highpower applications ranging from modern portable electronics to electric automotive. A battery-supercapacitor hybrid energy system is a power source that can meet the peak power demands in camera flashes, pulsed lasers, and computer systems back-up as well as electric propulsion in diverse industrial and vehicular transport applications. Among the materials systems, structured carbons which store charges as an electric double layer (EDL) in liquid electrolyte medium are widely studied with a focus on overcoming the energy-density limitation [1]. The materials systems which show capacitive function based on redox reactions are the insertion-type metal oxides and doped-conducting polymers capable of high energy-density storage [2,3]. The conducting polymers, such as polypyrrole (PPy), poly(3,4 ethylenedioxythiophene) (PEDOT), and polyaniline (PANI) which undergo redox processes equivalent of doping and dedoping of electrolyte ions as means of energy storage are being aggressively studied. These polymers exhibit pseudocapacitance properties due to presence of charge transfer reactions. The other most widely studied materials are the metal oxides RuO2, MnO2, V2O5, NiO, and Co3O4 which show highly capacitive behavior due to reversible and fast surface redox reactions with electrolyte ions [2,4]. In the recent years, conducting polymers with a nanoporous morphology and as nanocomposites with metaloxides have emerged as the materials system of great potential for high energy-density storage. Electrodes based on these materials structured at the nanoscale enable many-fold enhancements of the electroactive surface and interface with electrolyte facilitating absorption, ingress, and diffusion of electrolyte ions which being the main energy storage units could lead to increased energy and power density of supercapacitor devices. The high surface area morphology in conducting polymers is attained by creating variations in its nanostructure like nanoporous [5], nanofibers [6,7], nanowires [8], nanobelts [9], and by size-selective nanopores in the context of c (...truncated)


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Navjot Kaur Sidhu, Alok C Rastogi. Vertically aligned ZnO nanorod core-polypyrrole conducting polymer sheath and nanotube arrays for electrochemical supercapacitor energy storage, Nanoscale Research Letters, 2014, pp. 453, Volume 9, Issue 1, DOI: 10.1186/1556-276X-9-453